Hydrogen diffusion apparatus



July 16, 196s H, KOCH JR 3,392,510

HYDROGEN DIFFUSION APPARATUS Filed April 1, 1965 INVENTOR fa/777 H Koch, Jr:

United States Patent Office 3,392,510 HYDROGEN DIFFUSION APPARATUS John H. Koch, Jr., Nntley, NJ., assignor to Engelhard Industries, Inc., Newark, NJ., a corporation of Delaware Filed Apr. 1, 1965, Ser. No. 444,656 1 Claim. (Cl. 55-158) The present invention relates to hydrogen purification apparatus and particularly to an improved unit for purification of hydrogen by diffusion through a non-porous hydrogen-permeablqmetal.

It is well known to purify hydrogen by diffusion through a thin wall of nou-porous hydrogen-pereable metal. Impure gas containing hydrogen is brought into contact with the metal wall under heat and pressure and only pure hydrogen permeates the wall and diffuses through it.

Known hydrogen-permeable metals include palladium and palladium alloys such as palladium-silver and palladium-nickel. A suitable palladium-silver binary alloy contains 25% by weight silver.

One form of apparatus used to purify hydrogen by the diffusion process employs a bundle of thin-walled tubes of palladium alloy, fixedly supported at the ends within a collection chamber. Impure feed gas containing hydrogen is fed into the bores of the tubes, and hydrogen which diffuses through the tube walls is collected in and removed from the surrounding chamber. In such apparatus, heating means is ordinarily provided since hydrogen diffusion through palladium alloys is ordinarily effected at elevated temperature, e.g., 300 to 600 C.

For efficiency in the use of palladium or palladium -alloy diffusion tubes, wall thicknesses between about 3 mils and 6 mils are employed. Because of the expansion and contraction of the thin-walled metal tubes due to hydrogen adsorption and removal :as well as dimensional changes due to thermal stresses which occur on heating and cooling, there is great stress on the tubes and joints between tubes and headers, resulting in failure particularly at the joints.

In accordance with the present invention, apparatus is provided in which problem of failure of palladium and palladium alloy hydrogen tube diffusers due to stresses from heating and cooling in the presence of hydrogen is minimized. The hydrogen diffuser consists of a bundle of straight tubes open on each end to headers or tube sheets to which the tubes are welded or brazed securely. Each header consists of a chamber, which may be cylindrical in cross section, one wall of which is the sheet containing multiple open tube ends, and the other wall containing a single attached tube opening, preferably in central position, to which coiled inlet and outlet tubes are attached. Such coiled tubes or pigtails provide the sole fixed support for the tube bundle within an outer collection chamber and, in order to relieve stresses, each coiled tube is spirally coiled in opposite direction. The tube assembly moves freely in a cylindrical pressure vessel with closed ends, the coils passing through the center of the respective ends of the pressure vessel. Feed gas enters the tube bundle at one end, diffusion takes place through the straight diffusion tubes and undiffused gas passes off through the coil at the other end of the tube bundle. Diffused pure hydrogen is removed from the pressure vessel chamber.

The apparatus of the present invention is more fully described below with reference to the attached drawing which shows the apparatus in section.

Referring to the drawing, the apparatus of the invention consists of a diffusion cell 10 comprising at least one diffusion tube 11 of non-porous hydrogen-permeable metal such as palladium alloyed with silver. The diffusion Patented July 16, 1968 tubes 11 are attached between and open into cylindrical headers 12 and 12', and the tubes and headers are enclosed in a cylindrical vessel 13. At one end of the cell, an inlet tube 14 has one end connected to and opening into one of the headers 12 and its other end opening outside the vessel 13. Inlet tube 14 is of coiled, or pigtail configuration coiled either in a clockwise or counter clockwise direction. Similarly, an exhaust tube 16 at the other end of the tube bundle is connected to the other header 12' and opens outside the tank. Exhaust tube 16 is also of coiled configuration, but coiled in a direction opposite to that of inlet tube 14.

The diffusion cell 10 is heated by electric heating elements 18 adjacent the outside of vessel 13. Outlet tube 19 in vessel 13 is provided for removal of diffused pure hydrogen.

In the operation of the diffusion cell, impure gas containing hydrogen is fed into the inlet tube 14 at one end and flows through the adjacent header 12, through the tubes 11 to the other header 12' and out of the cell through the exhaust tube 16 which may be provided with a valve to control rate of the gas flow. As the gas mixture passes through the tubes 11, hydrogen permeates and diffuses through the walls of the tubes 11 into vessel 13 from which it is removed by outlet tube 19.

It will be understood from the above that the sole points of fixed connection between the tube bundle and header, and the collection vessel 13, are at the points where the inlet tube 14 and the outlet tube 16 enter the vessel 13. Thus, any strain due to twisting or expansion of the diffusion tubes 11 is taken up by the coiled inlet and outlet tubes.

While the diffusion tubes are of palladium or palladium alloy, the remaining cell parts are suitably of stainless steel. The diffusion tubes with the header chambers and the two pigtails are first assembled with the pigtails in stretched position. The pigtails are usually of equal diameter and length, although the inlet pigtail may be of larger bore, This sub-assembly is then sealed to the jacketing chamber. Assembly with the pigtails in stretched position assists in countering the tendency to lengthening of the coils on providing internal gas pressure due to Bourdon tube effect and the tendency to stretching of the pigtails due to greater expansion of the stainless steel than the palladium alloys on heating to 300 to 600 C. in operation of the unit.

The apparatus of the present invention may be employed in horizontal or vertical position, but vertical positioning of the assembly may be preferable because movement by sagging is minimized and also because less Hoor space is then required.

While the apparatus of the invention has been described above in connection with a particular embodiment thereof, it will be appreciated that some modifications may be made in the structure and arrangement without departing from the spirit and scope of the invention as defined by the following claim.

1. A hydrogen purification unit comprising an outer vessel, a plurality of thin-walled palladium-containing diffusion tubes supported at each end by a tube sheet, each of said tube sheets comprising one Wall of a header composed of spaced walls defining a chamber, the opposite wall of each tube header having an opening and attached thereto a single coiled tube, one of said coiled tubes being coiled in a clockwise direction, and the other in a counter clockwise direction, the said diffusion tubes and attached headers being enclosed within said outer vessel and fixedly supported therein solely by attachment to each of said coiled tubes.

(References on following page) References Cited UNITED FOREIGN PATENTS STATES PATENTS 667,016 7/1963 Canada.

Green et al 55 158 1,178,480 12/ 1958 France.

Tillyer et a1 55-16 Rudd n 55-158 X 5 REUBIN FRIEDMAN, Przmary Exammer. Ehlers et al. 55-158 J. W. ADEE, Assistant Examiner.

Rubin 55-158 

1. A HYDROGEN PURIFICATION UNIT COMPRISING AN OUTER VESSEL, A PLURALITY OF THIN-WALLED PALLADIUM-CONTAINING DIFFUSION TUBES SUPPORTED AT EACH END BY A TUBE SHEET, EACH OF SAID TUBE SHEETS COMPRISING ONE WALL OF A HEADER COMPOSED OF SPACED WALLS DEFINING A CHAMBER, THE OPPOSITE WALL OF EACH TUBE HEADER HAVING AN OPENING AND ATTACHED THERETO A SINGLE COILED TUBE, ONE OF SAID COILED TUBES BEING COILED IN A CLOCKWISE DIRECTION AND THE OTHER IN A COUNTER CLOCKWISE DIRECTION, THE SAID DIFFUSION TUBES AND ATTACHED HEADERS BEING ENCLOSED WITHIN SAID OUTER VESSEL AND FIXEDLY SUPPORTED THEREIN SOLELY BY ATTACHMENT TO EACH OF SID COILED TUBES. 